Don’t have an objective definition of “Best” but here are few over the top of my head.
Profiled backend’s startup and reduced startup time by ~20-30 times. Issue was we were traversing node_modules folder to scan for API documentation.
Profiled python using cProfiler & snakeviz and optimized dozens of regex calls by simple pre-filtering. Improved performance by ~20 times.
Profiled python using pprofile & qcalgrind (IIRC) to pinpoint a single heavy regex compilation and optimized it by pre-filtering. Improved performance 8-10 times.
Use nodejs streams to do load data from s3, parse as CSV, transform into different structure and save into s3 in a continuous stream. Didn’t measure the performance gains but should be several times atleast. 5… many more, some coming from embedded world and even more drastic & unexpected